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# SparseArray

`public class SparseArray`
`extends Object` `implements Cloneable`

java.lang.Object
↳ | android.util.SparseArray<E>

`SparseArray` maps integers to Objects and, unlike a normal array of Objects, its indices can contain gaps. `SparseArray` is intended to be more memory-efficient than a `HashMap`, because it avoids auto-boxing keys and its data structure doesn't rely on an extra entry object for each mapping.

Note that this container keeps its mappings in an array data structure, using a binary search to find keys. The implementation is not intended to be appropriate for data structures that may contain large numbers of items. It is generally slower than a `HashMap` because lookups require a binary search, and adds and removes require inserting and deleting entries in the array. For containers holding up to hundreds of items, the performance difference is less than 50%.

To help with performance, the container includes an optimization when removing keys: instead of compacting its array immediately, it leaves the removed entry marked as deleted. The entry can then be re-used for the same key or compacted later in a single garbage collection of all removed entries. This garbage collection must be performed whenever the array needs to be grown, or when the map size or entry values are retrieved.

It is possible to iterate over the items in this container using `keyAt(int)` and `valueAt(int)`. Iterating over the keys using `keyAt(int)` with ascending values of the index returns the keys in ascending order. In the case of `valueAt(int)`, the values corresponding to the keys are returned in ascending order.

## Summary

### Public constructors
`SparseArray()` Creates a new SparseArray containing no mappings.
`SparseArray(int initialCapacity)` Creates a new SparseArray containing no mappings that will not require any additional memory allocation to store the specified number of mappings.

### Public methods
`void` | `append(int key, E value)` Puts a key/value pair into the array, optimizing for the case where the key is greater than all existing keys in the array.
`void` | `clear()` Removes all key-value mappings from this SparseArray.
`SparseArray<E>` | `clone()` Creates and returns a copy of this object.
`boolean` | `contains(int key)` Returns true if the key exists in the array.
`void` | `delete(int key)` Removes the mapping from the specified key, if there was any.
`E` | `get(int key)` Gets the Object mapped from the specified key, or `null` if no such mapping has been made.
`E` | `get(int key, E valueIfKeyNotFound)` Gets the Object mapped from the specified key, or the specified Object if no such mapping has been made.
`int` | `indexOfKey(int key)` Returns the index for which `keyAt(int)` would return the specified key, or a negative number if the specified key is not mapped.
`int` | `indexOfValue(E value)` Returns an index for which `valueAt(int)` would return the specified value, or a negative number if no keys map to the specified value.
`int` | `keyAt(int index)` Given an index in the range `0...size()-1`, returns the key from the `index`th key-value mapping that this SparseArray stores.
`void` | `put(int key, E value)` Adds a mapping from the specified key to the specified value, replacing the previous mapping from the specified key if there was one.
`void` | `remove(int key)` Alias for `delete(int)`.
`void` | `removeAt(int index)` Removes the mapping at the specified index.
`void` | `removeAtRange(int index, int size)` Remove a range of mappings as a batch.
`void` | `setValueAt(int index, E value)` Given an index in the range `0...size()-1`, sets a new value for the `index`th key-value mapping that this SparseArray stores.
`int` | `size()` Returns the number of key-value mappings that this SparseArray currently stores.
`String` | `toString()` Returns a string representation of the object. This implementation composes a string by iterating over its mappings.
`E` | `valueAt(int index)` Given an index in the range `0...size()-1`, returns the value from the `index`th key-value mapping that this SparseArray stores.

### Inherited methods
From class `java.lang.Object`
`Object` | `clone()` Creates and returns a copy of this object.
`boolean` | `equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void` | `finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>` | `getClass()` Returns the runtime class of this `Object`.
`int` | `hashCode()` Returns a hash code value for the object.
`final void` | `notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void` | `notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String` | `toString()` Returns a string representation of the object.
`final void` | `wait(long timeout, int nanos)` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed.
`final void` | `wait(long timeout)` Causes the current thread to wait until either another thread invokes the `notify()` method or the `notifyAll()` method for this object, or a specified amount of time has elapsed.
`final void` | `wait()` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object.

## Public constructors

### SparseArray

    public SparseArray ()

Creates a new SparseArray containing no mappings.

### SparseArray

    public SparseArray (int initialCapacity)

Creates a new SparseArray containing no mappings that will not require any additional memory allocation to store the specified number of mappings. If you supply an initial capacity of 0, the sparse array will be initialized with a light-weight representation not requiring any additional array allocations.

Parameters
`initialCapacity` | `int`

## Public methods

### append

    public void append (int key,
                    E value)

Puts a key/value pair into the array, optimizing for the case where the key is greater than all existing keys in the array.

Parameters
`key` | `int`
`value` | `E`

### clear

    public void clear ()

Removes all key-value mappings from this SparseArray.

### clone

    public SparseArray<E> clone ()

Creates and returns a copy of this object. The precise meaning of "copy" may depend on the class of the object. The general intent is that, for any object `x`, the expression:

>      x.clone() != x

will be true, and that the expression:

>      x.clone().getClass() == x.getClass()

will be `true`, but these are not absolute requirements. While it is typically the case that:

>      x.clone().equals(x)

will be `true`, this is not an absolute requirement.

By convention, the returned object should be obtained by calling `super.clone`. If a class and all of its superclasses (except `Object`) obey this convention, it will be the case that `x.clone().getClass() == x.getClass()`.

By convention, the object returned by this method should be independent of this object (which is being cloned). To achieve this independence, it may be necessary to modify one or more fields of the object returned by `super.clone` before returning it. Typically, this means copying any mutable objects that comprise the internal "deep structure" of the object being cloned and replacing the references to these objects with references to the copies. If a class contains only primitive fields or references to immutable objects, then it is usually the case that no fields in the object returned by `super.clone` need to be modified.

The method `clone` for class `Object` performs a specific cloning operation. First, if the class of this object does not implement the interface `Cloneable`, then a `CloneNotSupportedException` is thrown. Note that all arrays are considered to implement the interface `Cloneable` and that the return type of the `clone` method of an array type `T[]` is `T[]` where T is any reference or primitive type. Otherwise, this method creates a new instance of the class of this object and initializes all its fields with exactly the contents of the corresponding fields of this object, as if by assignment; the contents of the fields are not themselves cloned. Thus, this method performs a "shallow copy" of this object, not a "deep copy" operation.

The class `Object` does not itself implement the interface `Cloneable`, so calling the `clone` method on an object whose class is `Object` will result in throwing an exception at run time.

Returns
`SparseArray<E>` | a clone of this instance.

### contains

    public boolean contains (int key)

Returns true if the key exists in the array. This is equivalent to `indexOfKey(int)` >= 0.

Parameters
`key` | `int`: Potential key in the mapping

Returns
`boolean` | true if the key is defined in the mapping

### delete

    public void delete (int key)

Removes the mapping from the specified key, if there was any.

Parameters
`key` | `int`

### get

    public E get (int key)

Gets the Object mapped from the specified key, or `null` if no such mapping has been made.

Parameters
`key` | `int`

Returns
`E` |

### get

    public E get (int key,
                    E valueIfKeyNotFound)

Gets the Object mapped from the specified key, or the specified Object if no such mapping has been made.

Parameters
`key` | `int`
`valueIfKeyNotFound` | `E`

Returns
`E` |

### indexOfKey

    public int indexOfKey (int key)

Returns the index for which `keyAt(int)` would return the specified key, or a negative number if the specified key is not mapped.

Parameters
`key` | `int`

Returns
`int` |

### indexOfValue

    public int indexOfValue (E value)

Returns an index for which `valueAt(int)` would return the specified value, or a negative number if no keys map to the specified value.

Beware that this is a linear search, unlike lookups by key, and that multiple keys can map to the same value and this will find only one of them.

Note also that unlike most collections' `indexOf` methods, this method compares values using `==` rather than `equals`.

Parameters
`value` | `E`

Returns
`int` |

### keyAt

    public int keyAt (int index)

Given an index in the range `0...size()-1`, returns the key from the `index`th key-value mapping that this SparseArray stores.

The keys corresponding to indices in ascending order are guaranteed to be in ascending order, e.g., `keyAt(0)` will return the smallest key and `keyAt(size()-1)` will return the largest key.

For indices outside of the range `0...size()-1`, the behavior is undefined for apps targeting `Build.VERSION_CODES.P` and earlier, and an `ArrayIndexOutOfBoundsException` is thrown for apps targeting `Build.VERSION_CODES.Q` and later.

Parameters
`index` | `int`

Returns
`int` |

### put

    public void put (int key,
                    E value)

Adds a mapping from the specified key to the specified value, replacing the previous mapping from the specified key if there was one.

Parameters
`key` | `int`
`value` | `E`

### remove

    public void remove (int key)

Alias for `delete(int)`.

Parameters
`key` | `int`

### removeAt

    public void removeAt (int index)

Removes the mapping at the specified index.

For indices outside of the range `0...size()-1`, the behavior is undefined for apps targeting `Build.VERSION_CODES.P` and earlier, and an `ArrayIndexOutOfBoundsException` is thrown for apps targeting `Build.VERSION_CODES.Q` and later.

Parameters
`index` | `int`

### removeAtRange

    public void removeAtRange (int index,
                    int size)

Remove a range of mappings as a batch.

Parameters
`index` | `int`: Index to begin at
`size` | `int`: Number of mappings to remove For indices outside of the range `0...size()-1`, the behavior is undefined.

### setValueAt

    public void setValueAt (int index,
                    E value)

Given an index in the range `0...size()-1`, sets a new value for the `index`th key-value mapping that this SparseArray stores.

For indices outside of the range `0...size()-1`, the behavior is undefined for apps targeting `Build.VERSION_CODES.P` and earlier, and an `ArrayIndexOutOfBoundsException` is thrown for apps targeting `Build.VERSION_CODES.Q` and later.

Parameters
`index` | `int`
`value` | `E`

### size

    public int size ()

Returns the number of key-value mappings that this SparseArray currently stores.

Returns
`int` |

### toString

    public String toString ()

Returns a string representation of the object. In general, the `toString` method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

The `toString` method for class `Object` returns a string consisting of the name of the class of which the object is an instance, the at-sign character ``@`', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

>      getClass().getName() + '@' + Integer.toHexString(hashCode())

This implementation composes a string by iterating over its mappings. If this map contains itself as a value, the string "(this Map)" will appear in its place.

Returns
`String` | a string representation of the object.

### valueAt

    public E valueAt (int index)

Given an index in the range `0...size()-1`, returns the value from the `index`th key-value mapping that this SparseArray stores.

The values corresponding to indices in ascending order are guaranteed to be associated with keys in ascending order, e.g., `valueAt(0)` will return the value associated with the smallest key and `valueAt(size()-1)` will return the value associated with the largest key.

For indices outside of the range `0...size()-1`, the behavior is undefined for apps targeting `Build.VERSION_CODES.P` and earlier, and an `ArrayIndexOutOfBoundsException` is thrown for apps targeting `Build.VERSION_CODES.Q` and later.

Parameters
`index` | `int`

Returns
`E` |

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